Abstract Abstract Background: Statins can cause tubular proteinuria by inhibiting tubular reabsorption of urinary proteins. To distinguish between microalbuminuria originating from glomerular leakage of albumin and tubular microalbuminuria due to statin therapy, the α1-microglobulin/albumin ratio is evaluated in patients taking statins and compared to untreated patients. Methods: Ten apparently healthy subjects were given 40 mg of simvastatin and tested for urinary α1-microglobulin, albumin, creatinine and cystatin C, up to 24 h after administration. Additionally, urine samples of 76 statin-treated and 456 untreated patients presenting with micro-albuminuria (albuminuria range between 20 and 200 mg/L) were tested for α1-microglobulin and albumin. α1-Microglobulin/albumin ratios were compared. Total cholesterol was measured in 50 patients on statin therapy. Results: In the 10 apparently healthy subjects, a significant temporary increase of α1-microglobulin, albumin and α1-microglobulin/albumin ratio was observed after statin intake. In the group of 532 patients showing micro-albuminuria, those treated with statins showed a significantly higher mean urinary α1-microglobulin/albumin ratio then untreated patients. Urinary albumin concentrations were significantly higher in patients taking simvastatin than in patients on rosuvastatin treatment and they were also higher in patients on statin therapy with a total serum cholesterol concentration below 3.88 mmol/L than in patients with a total serum cholesterol concentration above 5.17 mmol/L. Conclusions: Tubular proteinuria, caused by the use of statins, can be distinguished from glomerular proteinuria by a higher urinary α1-microglobulin/albumin ratio.